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A rectangular bird sanctuary is being created with one side along a straight riverbank. The remaining three sides (x, r parallel to the river, and another x) are to be enclosed with a protective fence that surrounds an area of 8 square kilometers (km'"2). Find the dimensions of the rectangle that minimize the amount of fencing (i.e., minimize the sum of the lengths of the three fenced sides of the sanctuary). ( river) 10 s -s O x = 2 km, r = 8 km O x = 8 km, r = 2 km O x = 4 km, r = 2 km O x = 2 km , 4 km